Re: Aquatic Plants Digest V2 #156

> From: eis at alto1_altonet.com (Paul Nicholson)
> Date: Fri, 23 Aug 1996 20:38:22 -0700
> Subject: Re: Triton Enhancers
> Merill Cohen said:
> >One thing that you both did not take into consideration is that "plain
> >old white" fades to yellow -- in both the paint and the plastic.
> >"Enhancers" remain the same -- only get dirty if you don't clean them!
> >When clean, they are like new.  You would have to repaint the "plain
> >old reflectors"! (IMHO)

Paul said:
> I think that depends on the paint you use. How many white cars have you
> seen that have turned yellow? Applliances hold their color too. I've got
> some old shoplight fixtures that are still white.

Baked on enamel is a fairly UV resistant material.  Most white paints are 
not.  I'm presently using a white two-part epoxy paint designed for 
refinishing appliances and tubs, and it is holding up fairly well after 6 
months of metal halide exposure.

White brush-on enamel exposed to light from metal halide lamps will 
yellow in fairly short order.

Specular aluminum has one potential advantage/disadvantage over white
enamel or white appliance epoxy that has not yet been discussed:  aluminum
has sustantially higher UV reflectivity than most paints.  On paper, the
most UV reflective white paint would be white, high titanium dioxide
content acrylic, but the problem with acrylic is that it is water-based,
and not tremendously durable in a wet environment.  Aluminum is reflective
into the far UV.  There will be no blue/violet falloff as there will with
some white paints. 

This is probably a bigger issue in a reef situation than in a planted 
tank, but chl does have a fairly strong absorption feature at around 420 
nm, and I'd like to hang onto that as much as possible.  If there is any 
yellowing in the paint, you will be losing reflectivity at the far end of 
the visible/PAR region.

It isn't an effect that you will ever see with a lux meter, because of the 
wavelength weighting scheme used for that unit.  The weight goes to zero 
at 400 nm, and is damned small at 420 nm.